1. Field of the Invention
The present invention relates to an organic electroluminescent device (OELD) and more particularly to a top emission type OELD device and a method of fabricating the same.
2. Discussion of the Related Art
A cathode ray tube (CRT) has been widely used as a display device. Recently, however, a flat panel display device, for example, a plasma display panel (PDP) device, a liquid crystal display (LCD) device and an OELD, is used as a display device instead of the CRT.
Among these flat panel display devices, the OELD has an advantage in thickness and weight because the OELD does not require a backlight unit. The OELD device is a self-emission type display device. In addition, with comparison to the LCD device, the OELD has excellent capabilities of a wide viewing angle, contrast ratio, low power consumption, past response time, and so on. Moreover, since a fabricating method for the OELD is simple, there is another advantage in production costs.
The OELD is classified into a passive matrix type and an active matrix type. In the active matrix type OELD, a thin film transistor (TFT) as a switching element is disposed at each pixel. Since the active matrix type OELD device has excellent capabilities of high resolution, low power consumption and lifetime with comparison to the passive matrix type OELD, the active matrix type OELD is much widely introduced.
FIG. 1 is a schematic cross-sectional view of the related art OELD. In FIG. 1, the OELD 10 includes a first substrate 1, a second substrate 2 and a seal pattern 20. The second substrate 2 faces the first substrate 1. The seal pattern 20 is disposed at edges of the first and second substrates 1 and 2 to seal a space between the first and second substrates 1 and 2.
On the first substrate 1, a driving TFT DTr is formed. In addition, an organic electroluminescent diode E is formed over the first substrate 1 to be electrically connected to the driving TFT DTr. The organic electroluminescent diode E includes a first electrode 3, which is connected to the driving TFT DTr, an organic emission layer 5, which is disposed on the first electrode 3, and a second electrode 7, which is disposed on the organic emission layer 5. The organic emission layer 5 includes first to third organic emission patterns 5a to 5c for respectively emitting red (R), green (G) and blue (B) colors. The first electrode 3 serves as an anode, and the second electrode 7 serves as a cathode.
On the second substrate 2, an absorbent pattern 13 for absorbing moisture is formed.
The OELD 10 is classified into a top emission type and a bottom emission type depending on a transporting direction of light from the organic emitting layer 5. The bottom emission type OELD, where light passes through the first substrate 1, has advantages in stability and freedom of fabricating process, while the top emission type OELD, where light passes through the second substrate 2, has advantages in aperture ratio and resolution. Considering theses facts, the top emission type OELD is widely researched and introduced. Unfortunately, the second electrode 7 as a cathode is disposed on the organic emitting layer 5, so that there is a limitation in a material for the second electrode 7. As a result, light transmittance through the second electrode 7 is limited such that an optical efficiency is decreased.
In addition, since both the driving TFT DTr and the organic electroluminescent diode E are formed on the first substrate 1, production yield is reduced. Namely, if there is a defective during the driving TFT fabricating process or the organic electroluminescent diode fabricating process, an undesired OELD 10 are produced.
To resolve these problems, a dual panel type OELD is introduced. In the dual panel type OELD, an array element, for example, the driving TFT, is formed on one substrate, while the organic electroluminescent diode is formed on the other substrate. Then, the driving TFT and the organic electroluminescent diode are electrically connected to each other using a contact spacer.
On the other hand, the seal pattern for sealing an inner space of the OELD is formed of polymer. When the OELD is heated or used for long times, contaminants, for example, moisture or gas, are penetrated into an inner space of the OELD through the seal pattern such that properties of the organic electroluminescent diode are degraded. Particularly, an emission property of the organic emitting layer is degraded, and a lifetime of the organic electroluminescent diode is reduced. In addition, a dark point appears on a display screen because of the contaminants. When an external force is applied on the OELD, there is a crack on the first and second electrodes of the organic electroluminescent diode or the driving TFT. As a result, an image is not displayed by a pixel, where the crack is generated, such that there are problems of brightness or a displaying image quality.